Portable communication devices, such as mobile phones, have been recently expected to have multifunction. Particularly according to start of terrestrial digital broadcasting creates new demand for watching television (TV) broadcasts on mobile phones. Japanese Patent Laid-Open Publication No. 2001-526483 and Japanese Patent Laid-Open Publication No. 2003-188952 disclose such multifunctional communication devices.
A conventional portable receiver will be described below. FIG. 22 is a block diagram of the conventional portable receiver.
Antenna 1 for a mobile phone receives a mobile-phone signal, a high frequency signal of about 850 MHz. Antenna 1 has a length of about ¼ wavelengths (about 70 mm) of the signal so as to have an impedance of 50 Ω at the frequency of the signal.
An output of antenna 1 is connected to transmitting/receiving section 2 outputting digital audio data obtained by demodulating the received mobile-phone. An output of transmitting/receiving section 2 is connected to signal processor 3 for converting the digital audio data output from transmitting/receiving section 2 into an analog audio signal and outputting the signal to audio output unit 4.
Rod antenna 5 for receiving TV signals is extendable to have a variable length so as to receive high frequency signals ranging from about 50 MHz, the lower limit frequency in a VHF broadcast band, to about 770 MHz, an upper limit frequency of the UHF broadcast band. Having the length adjusted to about ¼ wavelengths of a signal to be received, antenna 5 can receive TV broadcasts. Rod antenna 5, upon being extended, needs to have a length greater than about 100 cm in order to receive a signal of about 50 MHz, a lower limit frequency in the VHF broadcast band.
An output of rod antenna 5 is connected to input terminal 6 of matching unit 7. Output terminal 8 of matching unit 7 outputs a signal in a broadcast band (frequency band) containing a signal of a channel to be received. Electronic tuner 9 for TV reception provided between output terminal 8 and signal processor 3 selects a signals to be received in the broadcast band, demodulates the signal to be received, and outputs the demodulated signal to signal processor 3.
Signal processor 3 performs a signal processing, such as a demodulating process or an error correction process, for the demodulated signal so as to convert the demodulated signal into an analog audio signal 1 and an analog video signal. The analog audio signal is output as audio from audio output unit 4, while the analog video signal is output as an image to display 10.
Matching unit 7 will be described in detail below. Matching device 7 includes series assembly 13 having first switch 11 and low-pass filter 12, series assembly 16 having second switch 14 and band-pass filter 15, and series assembly 19 having third switch 17 and high-pass filter 18. Series assemblies 13, 16 and 19 are connected in parallel with each other.
A cut-off frequency of low-pass filter 12 is the highest frequency of channels in a VHF low band (90 MHz to 108 MHz in Japan, 55 MHz to 88 MHz in the U.S.). Band-pass filter 15 allows signals in a VHF high band (170 MHz to 222 MHz in Japan, 170 MHz to 216 MHz in the U.S.) to pass through it, and blocks signals of the other frequencies. A cut-off frequency of high-pass filter 18 is the lowest frequency of channels in a UHF band (470 MHz to 770 MHz in Japan, 470 MHz to 806 MHz in the U.S.).
In matching device 7, if a signal of a channel in the VHF low band is received, first switch 11 is exclusively turned on. This operation allows the signal to be supplied to low-pass filter 12, thus attenuating signals of frequencies higher than frequencies in the VHF low band. If a signal of a channel in the VHF high band is received, second switch 14 is exclusively turned on. This operation allows the signal to be supplied to band-pass filter 15, thus attenuating signals of frequencies other than frequencies in the VHF high band. If a signal of a channel in the UHF band is received, third switch 17 is exclusively turned on. This operation allows the signal to be supplied to high-pass filter 18, thus attenuating signals of frequencies other than the frequencies in the UHF band. Filters 12, 15 and 18 have a function to match impedances between rod antenna 5 and electronic tuner 9 for the signals of the frequencies supplied to the tuner.
Transmitting/receiving section 2 is required to be always ready to receive a signal input from antenna 1 so as to detect a mobile-phone signal whenever the phone signal is input. Transmitting/receiving section 2 transmits a signal periodically to a nearest base station (not illustrated) via antenna 1. Therefore, regardless of the cases that a TV broadcast is received or not, a signal is transmitted and received between transmitting/receiving section 2 and antenna 1.
The conventional portable device is not carried easily since including such separate antennas, antenna 1 for a mobile phone and antenna 5 for TV reception and accordingly having a large size and weight. In particular, Rod antenna 5 to receive TV broadcast signals has a large length of ¼ wavelengths of TV broadcast signals, thus preventing the portable device from being carried easily. For example, in order to receive VHF broadcasts (Channel 7 of VHF band in Japan), antenna 5 needs to have a length of about 40 cm.